The present application relates to VTOL vehicles with multi-function capabilities and, specifically to ducted fan arrangements that facilitate the flow of air during hover as well as forward flight of such vehicles, and the operation and behavior of these vehicles in restrictive environments and proximity to objects.
VTOL vehicles rely on direct thrust from propellers or rotors, directed downwardly, for obtaining lift necessary to support the vehicle in the air. Many different types of VTOL vehicles have been proposed where the weight of the vehicle in hover is carried directly by rotors or propellers, with the axis of rotation perpendicular to the ground. One well known vehicle of this type is the conventional helicopter which includes a large rotor mounted above the vehicle fuselage. Other types of vehicles rely on a multitude of propellers that are either exposed (e.g., unducted fans), or installed inside circular cavities, shrouds, ducts or other types of nacelle (e.g., ducted fans), where the flow of air takes place inside ducts. Some VTOL vehicles (such as the V-22) use propellers having their axes of rotation fully rotatable (up to 90 degrees or so) with respect to the body of the vehicle; these vehicles normally have the propeller axis perpendicular to the ground for vertical takeoff and landing, and then tilt the propeller axis forward for normal flight. Other vehicles use propellers having nearly horizontal axes, but include aerodynamic deflectors installed behind the propeller which deflect all or part of the flow downwardly to create direct upward lift.
A number of VTOL vehicles have been proposed in the past where two or four propellers, usually mounted inside ducts (i.e., ducted fans), were placed forwardly of, and rearwardly of, the main payload of the vehicle. One typical example is the Piasecki VZ-8 ‘Flying Jeep’ which had two large ducts, with the pilots located to the sides of the vehicle, in the central area between the ducts. A similar configuration was used on the Chrysler VZ-6 and on the CityHawk flying car. Also the Bensen ‘Flying Bench’ uses a similar arrangement. The Curtiss Wright VZ-7 and the Moller Skycar use four, instead of two, thrusters where two are located on each side (forward and rear) of the pilots and the payload, the latter being of fixed nature at the center of the vehicle, close to the vehicle's center of gravity.
The foregoing existing vehicles are generally designed for specific functions and are therefore not conveniently capable of performing a multiplicity of functions.
Patents owned by the present assignee that relate to VTOL vehicles include U.S. Pat. Nos. 6,464,166; 6,568,630, 6,817,570 and 6,883,748. The '570 patent discloses unique control vane arrangements including pivotally mounted vanes at both the inlet end and the outlet or exit end of the ducted fan units. A related pending application Ser. No. 11/411,243, filed Apr. 26, 2006, discloses duct and fuselage modification that facilitate air flow particularly during forward flight. For example, openings are provided in the forward and rearward duct walls to selectively allow air to enter the forward duct in a substantially horizontal flow direction and to exit the rearward duct in a direction with at least a horizontal flow component. In addition, fuselage shape changes enhance aerodynamic life, thus reducing the lift burden on the ducted fans.